Hopefully somebody here has experience with this. I use the lead core line for sink tips, the stuff i've used is T-8. I was reading this web page a guy wrote http://www.byrdultrafly.com/sublines.htm and he has a chart at the end. I'm using this stuff succesfully with a 6wt rod and haven't experienced any problems. I have 4 or 5 different length lines made up for what I assumed would make for the longer one sinking faster. He gives a sink rate time matching the grain line only. So does 8' sink at the same rate as 2 ft.
I like the stuff cause I can just remove it and fish surface with poppers or rubber spiders. Alot of places I just carry one rod and it's alot more multi purpose. Anybody with experience using this stuff and can clarify how much I should add to my line and explain why. This link has me confused where I once thought i knew what I was doing.
Al